Overworld boss

The Nether has the Wither, The End has the Ender Dragon, the Overworld has none. (Well, technically- 'cause the Warden and the Creaking kind of count?) Look- Wither is player-spawned, Ender Dragon is naturally-spawned. Why not have a Overworld boss that is MOB-spawned? (Like the snow golem- Endermen) The Wither and Ender Dragon are almost all black and white, so since the Overworld is MUCH safer, it could be mostly white and black. Both can fly too. The boss should be something able to be found in the Overworld, but a king, so I'm choosing birds.